Add History.TopHostsVisitsByRank UMA metric.

components/history/core/browser/url_utils.cc

Index: components/history/core/browser/url_utils.cc
diff --git a/components/history/core/browser/url_utils.cc b/components/history/core/browser/url_utils.cc
index a993619be392f9d842a1a11a0647b0494dab4b54..54dc5a9fc56cb61ed79634893f0ad3e17c3b2ac7 100644
--- a/components/history/core/browser/url_utils.cc
+++ b/components/history/core/browser/url_utils.cc
@@ -6,6 +6,7 @@
 
 #include <algorithm>
 
+#include "base/strings/string_util.h"
 #include "url/gurl.h"
 
 namespace history {
@@ -85,4 +86,12 @@ GURL ToggleHTTPAndHTTPS(const GURL& url) {
   return url.ReplaceComponents(replacement);
 }
 
+std::string HostForTopHosts(const GURL& url) {
+  std::string host = url.host();
+  base::StringToLowerASCII(&host);
+  if (base::StartsWith(host, "www.", base::CompareCase::SENSITIVE))
+    host.assign(host, 4, std::string::npos);
+  return host;
+}
+
 }  // namespace history